FuYeAI
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Comfort Fit Engine

Bra Size Intelligence Lab

Enter your underbust and overbust once to receive recommendations across 7 major sizing systems, plus sister sizes, measurement reminders, and fit tips.

AI-calibrated conversion tables tuned for Asian body profiles.

Automatic sister-size suggestions to fine-tune band and cup pairing.

Built-in measurement checklist so you can re-check posture anytime.

How to measure

Use a flexible tape, keep it parallel to the floor, relax your shoulders, and breathe normally. Stand in front of a mirror to confirm the tape sits flat on your back.

Underbust: wrap the tape beneath the bust, exhale gently before reading.
Overbust: pass the tape over the fullest point of the bust with neutral tension.
Measure without padded bras; a thin bralette or camisole works best.
Calibration log
Latest coefficients refreshed in Jan 2026
7Supported systems · US / UK / EU / JP etc.
280K+Recent sessions · In-tool measurements
2025.12Fit engine · Synced with boutique fittings
Enter measurement data
You can input decimal values; the unit switches automatically.

Measure twice and average for better stability.

Stand naturally—no shoulder lifting or stomach sucking.

Pick the system used by your favorite brand or retailer. You can switch anytime to compare.

Three-step measurement flow
Keep the tape level, relaxed, and steady.

Prep the tape

Measure at roughly the same time of day and average three readings.

Relax your posture

Look straight ahead, drop the shoulders, avoid puffing the chest.

Mind the units

Only have an inch tape? Enter inches directly—the tool converts for you.

Fit insight & helper cards
Your recommended size, sister sizes, and measurement log in one place.

Nothing here yet

Complete the form on the left and hit Calculate to see recommendations.

What is Bra Size Calculator

Two tape measurements, seven sizing systems: measure your underbust snugly at the bra band line on an exhale, then your bust at the fullest point, and the tool returns a starting size in US, UK, EU, JP and other systems at once — plus sister sizes and measuring-posture tips.

How to use Bra Size Calculator

  1. Measure your underbust (snug, at the breast root, on an exhale) and bust (fullest point)
  2. Enter both numbers in centimeters
  3. Compare the size across the seven systems and check sister-size options

Frequently asked questions

Why do sizes differ between brands and countries?

Band and cup letters follow different rules in each system — a 75B in Chinese sizing is roughly a 34B in US sizing. The calculator shows all seven systems side by side so you can match the brand's chart.

What is a sister size?

One band size up with one cup letter down (or the reverse) holds about the same cup volume — 75B and 70C, for example. If the band feels loose or tight, trying the sister size often fits better.

How accurate is the result?

Measuring error and breast shape both affect it, so treat the number as a starting point, not a verdict — trying bras on still beats any calculator. See a professional fitter if you're between sizes or uncomfortable.

Is Bra Size Calculator free?

Bra Size Calculator is completely free — open the page and use every feature with no hidden charges.

Do I need to download or install Bra Size Calculator?

No download or installation is needed. It is an online tool that runs in the browser on your phone, tablet and computer.

Do I need an account to use Bra Size Calculator?

No. Use the tool right away — no account or sign-in required.

Does Bra Size Calculator work on mobile?

Yes. The page is fully responsive and works on phones, tablets and desktop browsers.